bims-micesi 2023-09-10 papers

bims-micesi

Biomed News

on Mitotic cell signalling

Issue of 2023–09–10
nine papers selected by
Valentina Piano, Uniklinik Köln

Loss of the mitochondrial protein SPD-3 elevates PLK-1 levels and dysregulates mitotic events.
Dynamic Phosphorylation of G9a Regulates its Repressive Activity on Chromatin Accessibility and Mitotic Progression.
Polθ is phosphorylated by PLK1 to repair double-strand breaks in mitosis.
The role of centromeric repeats and transcripts in kinetochore assembly and function.
Distinctive phosphorylation pattern during mitotic exit network (MEN) regulation is important for the development and pathogenicity of Magnaporthe oryzae.
Mcl-1 deficiency in murine livers leads to nuclear polyploidisation and mitotic errors: Implications for hepatocellular carcinoma.
Crystal Structures of Plk1 Polo-Box Domain Bound to the Human Papillomavirus Minor Capsid Protein L2-Derived Peptide.
Vitrification induces a focused spindle pole in mouse MI oocytes.
RAD52 and ERCC6L/PICH have a compensatory relationship for genome stability in mitosis.

Life Sci Alliance. 2023 Nov;pii: e202302011. [Epub ahead of print]6(11):

Loss of the mitochondrial protein SPD-3 elevates PLK-1 levels and dysregulates mitotic events.

Yu-Zen Chen, Vitaly Zimyanin, Stefanie Redemann.

In metazoans, Polo-like kinase (PLK1) controls several mitotic events including nuclear envelope breakdown, centrosome maturation, spindle assembly and progression through mitosis. Here we show that a mutation in the mitochondria-localized protein SPD-3 affects mitotic events by inducing elevated levels of PLK-1 in early Caenorhabditis elegans embryos. SPD-3 mutant embryos contain abnormally positioned mitotic chromosomes, show a delay in anaphase onset and asymmetrically disassemble the nuclear lamina. We found that more PLK-1 accumulated on centrosomes, nuclear envelope, nucleoplasm, and chromatin before NEBD, suggesting that PLK-1 overexpression is responsible for some of the observed mitotic phenotypes. In agreement with this, the chromosome positioning defects of the spd-3(oj35) mutant could be rescued by reducing PLK-1 levels. Our data suggests that the mitochondrial SPD-3 protein affects chromosome positioning and nuclear envelope integrity by up-regulating the endogenous levels of PLK-1 during early embryogenesis in C. elegans This finding suggests a novel link between mitochondria and nuclear envelope dynamics and chromosome positioning by increasing the amount of a key mitotic regulator, PLK-1, providing a novel link between mitochondria and mitosis.

DOI: https://doi.org/10.26508/lsa.202302011
Adv Sci (Weinh). 2023 Sep 03. e2303224

Dynamic Phosphorylation of G9a Regulates its Repressive Activity on Chromatin Accessibility and Mitotic Progression.

Qizhi Geng, Yue-Yu Kong, Weizhe Li, Jianhao Zhang, Haoli Ma, Yuhang Zhang, Lin-Tai Da, Yan Zhao, Hai-Ning Du.

  Phosphorylation of Ser10 of histone H3 (H3S10p), together with the adjacent methylation of Lys9 (H3K9me), has been proposed to function as a 'phospho-methyl switch' to regulate mitotic chromatin architecture. Despite of immense understanding of the roles of H3S10 phosphorylation, how H3K9me2 are dynamically regulated during mitosis is poorly understood. Here, it is identified that Plk1 kinase phosphorylates the H3K9me1/2 methyltransferase G9a/EHMT2 at Thr1045 (pT1045) during early mitosis, which attenuates its catalytic activity toward H3K9me2. Cells bearing Thr1045 phosphomimic mutant of G9a (T1045E) show decreased H3K9me2 levels, increased chromatin accessibility, and delayed mitotic progression. By contrast, dephosphorylation of pT1045 during late mitosis by the protein phosphatase PPP2CB reactivates G9a activity and upregulates H3K9me2 levels, correlated with decreased levels of H3S10p. Therefore, the results provide a mechanistic explanation of the essential of a 'phospho-methyl switch' and highlight the importance of Plk1 and PPP2CB-mediated dynamic regulation of G9a activity in chromatin organization and mitotic progression.

Keywords:  G9a phosphorylation; Plk1, PPP2CB; chromatin accessibility; mitotic progression

DOI:  https://doi.org/10.1002/advs.202303224
Nature. 2023 Sep 06.

Polθ is phosphorylated by PLK1 to repair double-strand breaks in mitosis.

Camille Gelot, Marton Tibor Kovacs, Simona Miron, Emilie Mylne, Alexis Haan, Liza Boeffard-Dosierre, Rania Ghouil, Tatiana Popova, Florent Dingli, Damarys Loew, Josée Guirouilh-Barbat, Elaine Del Nery, Sophie Zinn-Justin, Raphael Ceccaldi.

DNA double-strand breaks (DSBs) are deleterious lesions that challenge genome integrity. To mitigate this threat, human cells rely on the activity of multiple DNA repair machineries that are tightly regulated throughout the cell cycle1. In interphase, DSBs are mainly repaired by non-homologous end joining and homologous recombination2. However, these pathways are completely inhibited in mitosis3-5, leaving the fate of mitotic DSBs unknown. Here we show that DNA polymerase theta6 (Polθ) repairs mitotic DSBs and thereby maintains genome integrity. In contrast to other DSB repair factors, Polθ function is activated in mitosis upon phosphorylation by Polo-like kinase 1 (PLK1). Phosphorylated Polθ is recruited by a direct interaction with the BRCA1 C-terminal domains of TOPBP1 to mitotic DSBs, where it mediates joining of broken DNA ends. Loss of Polθ leads to defective repair of mitotic DSBs, resulting in a loss of genome integrity. This is further exacerbated in cells that are deficient in homologous recombination, where loss of mitotic DSB repair by Polθ results in cell death. Our results identify mitotic DSB repair as the underlying cause of synthetic lethality between Polθ and homologous recombination. Together, our findings reveal the critical importance of mitotic DSB repair in the maintenance of genome integrity.

DOI: https://doi.org/10.1038/s41586-023-06506-6
Plant J. 2023 Sep 04.

The role of centromeric repeats and transcripts in kinetochore assembly and function.

Jothipriya Ramakrishnan Chandra, Manikandan Kalidass, Dmitri Demidov, Siarhei A Dabravolski, Inna Lermontova.

  Centromeres are the chromosomal domains, where the kinetochore protein complex is formed, mediating proper segregation of chromosomes during cell division. Although the function of centromeres has remained conserved during evolution, centromeric DNA is highly variable, even in closely related species. In addition, the composition of the kinetochore complexes varies among organisms. Therefore, it is assumed that the centromeric position is determined epigenetically, and the centromeric histone H3 (CENH3) serves as an epigenetic marker. The loading of CENH3 onto centromeres depends on centromere-licensing factors, chaperones, and transcription of centromeric repeats. Several proteins that regulate CENH3 loading and kinetochore assembly interact with the centromeric transcripts and DNA in a sequence-independent manner. However, the functional aspects of these interactions are not fully understood. This review discusses the variability of centromeric sequences in different organisms and the regulation of their transcription through the RNA Pol II and RNAi machinery. The data suggest that the interaction of proteins involved in CENH3 loading and kinetochore assembly with centromeric DNA and transcripts plays a role in centromere, and possibly neocentromere, formation in a sequence-independent manner.

Keywords:  RNA pol II; RNAi mechanism; centromere and kinetochore complex; centromeric transcripts; neocentromeres

DOI:  https://doi.org/10.1111/tpj.16445
Stress Biol. 2022 Sep 20. 2(1): 41

Distinctive phosphorylation pattern during mitotic exit network (MEN) regulation is important for the development and pathogenicity of Magnaporthe oryzae.

Wanzhen Feng, Jiansheng Wang, Xinyu Liu, Haowen Wu, Muxing Liu, Haifeng Zhang, Xiaobo Zheng, Ping Wang, Zhengguang Zhang.

  The mitotic exit network (MEN) pathway is a vital kinase cascade regulating the timely and correct progress of cell division. In the rice blast fungus Magnaporthe oryzae, the MEN pathway, consisting of conserved protein kinases MoSep1 and MoMob1-MoDbf2, is important in the development and pathogenicity of the fungus. We found that deletion of MoSEP1 affects the phosphorylation of MoMob1, but not MoDbf2, in contrast to what was found in the buddy yeast Saccharomyces cerevisiae, and verified this finding by in vitro phosphorylation assay and mass spectrometry (MS) analysis. We also found that S43 residue is the critical phosphor-site of MoMob1 by MoSep1, and proved that MoSep1-dependent MoMob1 phosphorylation is essential for cell division during the development of M. oryzae. We further provided evidence demonstrating that MoSep1 phosphorylates MoMob1 to maintain the cell cycle during vegetative growth and infection. Taken together, our results revealed that the MEN pathway has both distinct and conservative functions in regulating the cell cycle during the development and pathogenesis of M. oryzae.

Keywords:  Mitotic exit network (MEN); Pathogenicity; Phosphorylation; Rice blast

DOI:  https://doi.org/10.1007/s44154-022-00063-0
JHEP Rep. 2023 Oct;5(10): 100838

Mcl-1 deficiency in murine livers leads to nuclear polyploidisation and mitotic errors: Implications for hepatocellular carcinoma.

Laure-Alix Clerbaux, Pierre Cordier, Nina Desboeufs, Kristian Unger, Peter Leary, Gabriel Semere, Yannick Boege, Lap Kwan Chan, Chantal Desdouets, Massimo Lopes, Achim Weber.

   Background & Aims: Mcl-1, an antiapoptotic protein overexpressed in many tumours, including hepatocellular carcinoma (HCC), represents a promising target for cancer treatment. Although Mcl-1 non-apoptotic roles might critically influence the therapeutic potential of Mcl-1 inhibitors, these functions remain poorly understood. We aimed to investigate the effects of hepatic Mcl-1 deficiency (Mcl-1Δhep) on hepatocyte ploidy and cell cycle in murine liver in vivo and the possible implications on HCC.
Methods: Livers of young Mcl-1Δhep and wild-type (WT) mice were analysed for ploidy profile, mitotic figures, in situ chromosome segregation, gene set enrichment analysis and were subjected to two-thirds partial hepatectomy to assess Mcl-1 deficiency effect on cell cycle progression in vivo. Mcl-1Δhep tumours in older mice were analysed for ploidy profile, chromosomal instability, and mutational signatures via whole exome sequencing.
Results: In young mice, Mcl-1 deficiency leads to nuclear polyploidy and to high rates of mitotic errors with abnormal spindle figures and chromosome mis-segregation along with a prolonged spindle assembly checkpoint activation signature. Chromosomal instability and altered ploidy profile are observed in Mcl-1Δhep tumours of old mice as well as a characteristic mutational signature of currently unknown aetiology.
Conclusions: Our study suggests novel non-apoptotic effects of Mcl-1 deficiency on nuclear ploidy, mitotic regulation, and chromosomal segregation in hepatocytes in vivo. In addition, the Mcl-1 deficiency characteristic mutational signature might reflect mitotic issues. These results are of importance to consider when developing anti-Mcl-1 therapies to treat cancer.
Impact and implications: Although Mcl-1 inhibitors represent promising hepatocellular carcinoma treatment, the still poorly understood non-apoptotic roles of Mcl-1 might compromise their successful clinical application. Our study shows that Mcl-1 deficiency leads to nuclear polyploidy, mitotic errors, and aberrant chromosomal segregation in hepatocytes in vivo, whereas hepatocellular tumours spontaneously induced by Mcl-1 deficiency exhibit chromosomal instability and a mutational signature potentially reflecting mitotic issues. These results have potential implications for the development of anti-Mcl-1 therapies to treat hepatocellular carcinoma, especially as hyperproliferative liver is a clinically relevant situation.

Keywords:  Chromosome segregation; Hepatocarcinogenesis; Liver; Mcl-1; Mutational signature; Polyploidy

DOI:  https://doi.org/10.1016/j.jhepr.2023.100838
J Microbiol. 2023 Sep 08.

Crystal Structures of Plk1 Polo-Box Domain Bound to the Human Papillomavirus Minor Capsid Protein L2-Derived Peptide.

Sujin Jung, Hye Seon Lee, Ho-Chul Shin, Joon Sig Choi, Seung Jun Kim, Bonsu Ku.

  Human papillomaviruses (HPVs) can increase the proliferation of infected cells during HPV-driven abnormalities, such as cervical cancer or benign warts. To date, more than 200 HPV genotypes have been identified, most of which are classified into three major genera: Alphapapillomavirus, Betapapillomavirus, and Gammapapillomavirus. HPV genomes commonly encode two structural (L1 and L2) and seven functional (E1, E2, E4-E7, and E8) proteins. L2, the minor structural protein of HPVs, not only serves as a viral capsid component but also interacts with various human proteins during viral infection. A recent report revealed that L2 of HPV16 recruits polo-like kinase 1 (Plk1), a master regulator of eukaryotic mitosis and cell cycle progression, for the delivery of viral DNA to mitotic chromatin during HPV16 infection. In this study, we verified the direct and potent interactions between the polo-box domain (PBD) of Plk1 and PBD-binding motif (S-S-pT-P)-containing phosphopeptides derived from L2 of HPV16/HPV18 (high-risk alphapapillomaviruses), HPV5b (low-risk betapapillomavirus), and HPV4 (low-risk gammapapillomavirus). Subsequent structural determination of the Plk1 PBD bound to the HPV18 or HPV4 L2-derived phosphopeptide demonstrated that they interact with each other in a canonical manner, in which electrostatic interactions and hydrogen bonds play key roles in sustaining the complex. Therefore, our structural and biochemical data imply that Plk1 is a broad binding target of L2 of various HPV genotypes belonging to the Alpha-, Beta-, and Gammapapillomavirus genera.

Keywords:  Crystal structure; HPV18; HPV4; Human papillomavirus; L2; PBD; Plk1; Polo-box domain

DOI:  https://doi.org/10.1007/s12275-023-00071-3
Theriogenology. 2023 Aug 26. pii: S0093-691X(23)00325-4. [Epub ahead of print]211 232-240

Vitrification induces a focused spindle pole in mouse MI oocytes.

Yaoyao Guo, Haowei Sun, Hui Chen, Gongshe Yang, Jialun Wang, Zhengjun Qi, Weijun Pang, Guiyan Chu, Lei Gao.

  Immature oocyte (germinal vesicle stage, GV) vitrification can avoid a cycle of ovarian stimulation, which is friendly to patients with hormone-sensitive tumors. However, the in vitro maturation of vitrification-thawed GV oocyte usually results in aneuploidy, and the underlying mechanism remains unclear. Stable spindle poles are important for accurate chromosome segregation. Acentriolar microtubule-organizing centers (aMTOCs) undergo fragmentation and reaggregation to form spindle poles. Microtubule nucleation is facilitated via the perichromosome Ran after GVBD, which plays an important role in aMTOCs fragmentation. This study showed that vitrification may reduce microtubule density by decreasing perichromosomal Ran levels, which reduced the localization of pKIF11, thereby decreased the fragmentation of aMTOCs and formed a more focused spindle pole, ultimately resulted in aneuploidy. This study revealed the mechanism of abnormal spindle pole formation in vitrified oocytes and offered a theoretical support to further improve the quality of vitrified oocytes.

Keywords:  Microtubules; Oocyte vitrification; Ran; Spindle pole; aMTOCs

DOI:  https://doi.org/10.1016/j.theriogenology.2023.08.020
bioRxiv. 2023 Aug 23. pii: 2023.08.23.554522. [Epub ahead of print]

RAD52 and ERCC6L/PICH have a compensatory relationship for genome stability in mitosis.

Beth Osia, Arianna Merkell, Felicia Wednesday Lopezcolorado, Xiaoli Ping, Jeremy M Stark.

The mammalian RAD52 protein is a DNA repair factor that has both strand annealing and recombination mediator activities, yet is dispensable for cell viability. To characterize genetic contexts that reveal dependence on RAD52 to sustain cell viability (i.e., synthetic lethal relationships), we performed genome-wide CRISPR knock-out screens. Subsequent secondary screening found that depletion of ERCC6L in RAD52-deficient cells causes reduced viability and elevated genome instability, measured as accumulation of 53BP1 into nuclear foci. Furthermore, loss of RAD52 causes elevated levels of anaphase ultrafine bridges marked by ERCC6L, and conversely depletion of ERCC6L causes elevated RAD52 foci both in prometaphase and interphase cells. These effects were enhanced with combination treatments using hydroxyurea and the topoisomerase IIα inhibitor ICRF-193, and the timing of these treatments are consistent with defects in addressing such stress in mitosis. Thus, loss of RAD52 appears to cause an increased reliance on ERCC6L in mitosis, and vice versa. Consistent with this notion, combined depletion of ERCC6L and disrupting G2/M progression via CDK1 inhibition causes a marked loss of viability in RAD52-deficient cells. We suggest that RAD52 and ERCC6L play compensatory roles in protecting genome stability in mitosis.

DOI: https://doi.org/10.1101/2023.08.23.554522